Contents

Introduction

This document describes what type of network traffic for which the
Content Services Switch (CSS) 11000 will or will not map a flow.

Q.
What is a flow?

A. A flow is a stream of data traveling between two endpoints across a
network. For example, from one LAN station to another.

Q.
What is mapped as a flow?

A. Only Transmission Control Protocol (TCP) and User Datagram Protocol
(UDP) traffic are mapped as flows.

Q.
What is not mapped as a flow?

A. IP Security (IPSec) traffic that includes embedded TCP or UDP is not
mapped as a flow. Internet Control Message Protocol (ICMP) is never mapped as a
flow, however, CSS 11000 does pay attention to ICMP frames so that it can
properly associate them with a flow to do Network Address Translation (NAT),
where appropriate. The eventual recipient gets the proper IP information back.
This is particularly important for path Maximum Transmission Unit (MTU)
discovery support. When you are trying to adjust the TCP Maximum Segment Size
(MSS), you have to be aware of what session you are working in.

Below is the list of port numbers (UDP or TCP) that the CSS does not
setup a flow for. If a packet is received by the CSS with either a source or
destination port which matches one of the ones below, the frame is routed. A
flow is not setup.

Port

Description

67

BOOTP server

68

BOOTP client

137

NetBIOS name service

138

NetBIOS datagram service

161

SNMP

162

SNMP Traps

520

RIP

8089

Inktomi

Traceroute does not work in this manner. Different platforms use the
traceroute function in different methods (UDP, ICMP, and so on), and it is not
the port number alone that signifies which traffic is a traceroute packet. The
CSS does not setup flows for ICMP packets. Use the following guidelines to
determine if a traceroute packet will setup a flow:

The protocol is UDP.

The source port is > 32769.

The destination port is > 33434

The UDP data length is > 20

There is 1 byte sequence number in UDP portion.

There is 1 byte original Time To Live
(TTL).

If all these conditions are present, a flow is not setup for this
packet.